A variety of commercial chemical and petrochemical processes involve the condensation reaction of an olefin or a mixture of olefins over an acid catalyst to form higher molecular weight products. This type of condensation reaction is referred to herein as a polymerization process, and the products can be either low molecular weight oligomers or high molecular weight polymers. Oligomers are formed by the condensation of 2, 3 or 4 olefin molecules with each other, while polymers are formed by the condensation of 5 or more olefin molecules with each other. As used herein, the term "polymerization" is used to refer to a process for the formation of oligomers and/or polymers.
Low molecular weight olefins (such as propene, 2-methylpropene, 1-butene and 2-butene) can be converted by polymerization over a solid acid catalyst (such as a solid phosphoric acid catalyst) to a product which is comprised of oligomers and is of value as a high-octane gasoline blending stock and as a starting material for the production of chemical intermediates and end-products which include alcohols, detergents and plastics. Such a process is typically carried out over a fixed bed of solid acid catalyst at elevated temperatures and pressures in either a chamber reactor or a tubular reactor. A plurality of reactors is ordinarily used in the practice of such a process so that individual reactors can be taken out of service for catalyst replacement or other maintenance without shutting down the other reactors of the process unit. In addition, reaction conditions in the process unit may be optimized through the use of two or more reactors in series.
The acid catalyzed alkylation of aromatic compounds with olefins is a well-known reaction which is of commercial importance. For example, ethylbenzene, cumene and detergent alkylate are produced by the alkylation of benzene with ethylene, propylene and C.sub.10 to C.sub.8 olefins, respectively. Sulfuric acid, HF, phosphoric acid, aluminum chloride, and boron fluoride are conventional catalysts for this reaction. In addition, solid acids which have comparable acid strength can also be utilized to catalyze this process, and such materials include amorphous and crystalline aluminosilicates, clays, ion-exchange resins, mixed oxides and supported acids such as solid phosphoric acid catalysts.
When a fixed bed of solid acid catalyst is used to catalyze the polymerization of olefins, the catalyst typically undergoes a slow deactivation. In addition, catalyst deactivation is sometimes accompanied by an increased pressure drop through the catalyst bed. Deactivation is observed as a loss of catalyst activity with the passage of time, and it typically results from the formation of by-products which accumulate on the surface of the catalyst and in catalyst pores. These by-products have the effect of encapsulating the catalyst, thereby hindering or preventing fresh reactants in the feedstock from contacting the catalyst. Any increase in the pressure drop across the catalyst bed, which accompanies catalyst deactivation, is typically a result of the deposit of by-products in the void space between catalyst particles. After a certain level of catalyst deactivation and/or increase in pressure drop across the catalyst bed takes place, economic considerations generally require either that the catalyst be regenerated or that it be replaced with fresh catalyst.
The choice between replacement and regeneration of deactivated catalyst depends on a number of factors which include the cost of fresh catalyst, the disposal cost of deactivated catalyst if it is to be discarded, and the cost and effectiveness of catalyst regeneration procedures. A particularly important consideration is the amount of time that the polymerization unit must be taken out of service in order to replace or regenerate deactivated catalyst. The shutdown of a polymerization unit for such a purpose ordinarily carries a significant economic penalty and, accordingly, any shutdown period must be minimized.
In the case of an olefin polymerization unit which is operated with a solid phosphoric acid catalyst, deactivated catalyst is ordinarily discarded and replaced with fresh catalyst. The solid phosphoric acid catalyst is relatively inexpensive, and satisfactory regeneration options are typically not available for this type of catalyst. Accordingly, economic considerations generally dictate a replacement of the catalyst rather than regeneration.
U.S. Pat. No 4,028,430 (Stine et al.) is directed to a continuous catalytic reaction process utilizing a simulated moving catalyst bed to effect, simultaneously, a catalyzed reaction in one zone and catalyst reactivation in another zone of a catalyst bed which contains at least three zones. The zones are arranged in series with a fluid flow path connecting each adjacent zone and also connecting the first and last zones in the series. By periodic alteration of the composition of the fluids that are passed into each zone, the site of the catalyzed reaction and the location of catalyst reactivation can be periodically moved from one zone to the next in the series to provide a simulated moving catalyst bed process. It is disclosed that the process can be applied to catalyzed reactions such as alkylation, diolefin saturation, hydrocracking, catalytic cracking, desulfurization, dehydrogenation, polymerization, isomerization, reforming, and flue gas desulfurization. It is further disclosed that one suitable type of reactivation involves flushing tars, polymers, high molecular weight hydrocarbons, residue, or particulate matter out of a catalyst with a suitable dissolving or flushing agent.
Canadian Patent No. 1,055,921 (Burton et al.) discloses that a bed of solid phosphoric acid catalyst which has been deactivated by the deposition on the catalyst particles of polymerized and carbonized hydrocarbonaceous materials can be reactivated in situ by: (a) inundating the deactivated catalyst at a temperature of 40.degree. to 370.degree. C. and a pressure of 1 and 1/3 to 100 atmospheres, absolute, in a reactivating liquid mixture of hydrocarbons which is substantially free from sulfur, which contains at least 5 weight percent aromatics and which boils within the range of 40.degree. to 230.degree. C.; (b) withdrawing the reactivating liquid from the catalyst; and (c) repeating steps (a) and (b) above at least one time. It is further disclosed that a catalytic reformate can be used as the reactivating liquid, and that the deactivated catalyst can be from a polymerization unit which is used for the production of motor fuel from light olefinic gases. U.S. Pat. No. 4,062,801 (Burton et al.) discloses a similar process which involves regenerating a bed of deactivated catalyst through the use of a cycle of the following steps, wherein the cycle is carried out three times: (1) immersing the catalyst bed in a hot, aromatic hydrocarbon-containing liquid by passing the liquid upward into the catalyst bed; (2) soaking the catalyst bed in the liquid for at least 30 minutes at a temperature above about 280.degree. F.; and (3) draining the liquid from the catalyst.
U.S. Pat. No. 5,648,579 (Kulprathipanja et al.) is directed to a continuous process for conducting a catalyzed reaction in a single fixed bed of catalyst wherein catalyst deactivation is prevented through the use of periodic regeneration cycles, and wherein a regeneration cycle involves washing deactivating materials from the catalyst with a desorbent. The catalyzed reaction itself is terminated during each regeneration cycle by terminating the flow of one or more of the reactants. When applied to the alkylation of aromatics with olefins, the process is characterized by: (1) a reaction cycle, when both olefin and aromatic flow into the catalyst zone to effect alkylation, and (2) a flush cycle when only a desorbent flows into the catalyst zone. It is disclosed that this type of process can be applied to the alkylation of aromatics with alkylating agents, the alkylation of C.sub.3 -C.sub.6 olefins with alkanes in the C.sub.4 -C.sub.6 range, olefin hydration, ether formation by reaction of olefins with alcohols, and ester formation by reaction of organic acids with alcohols.